The present invention relates to a method for evoking, recording and analyzing event-related potentials (ERP), and more particularly to a method of measuring and determining P3 responses from a repeatedly presented stimulus or stimuli interspersed with non-significant stimuli and analyzing the measured ERP responses by means of a computer.
An electroencephalograph (EEG) is a device which measures and records brainwave activity by sensing spontaneous electrical potential of a person's scalp, cortex or cerebrum at various sites. Each EEG channel corresponds to particular electrode combination attached to the subject or patient. The sensed EEG potential at each channel is amplified by a differential amplifier, and the amplifier output signal is typically used to control movement of the recording pen of a polygraph. The EEG record is a long strip of polygraph paper containing a wave form for each EEG channel. The polygraph paper is driven at a predetermined rate (e.g., 30 millimeters per second) and is graduated to represent predetermined time increments. A skilled neurologist must evaluate the EEG record to determine abnormalities in the EEG wave forms.
EEG signals exhibit different frequencies depending upon varying activity. The EEG signal frequencies are classified into four basic frequency bands, which are generally referred to as "Delta" (0.3.5 Hertz); "Theta" (4 to less than 8 Hertz); "Alpha" (8-13 Hertz); and "Beta" greater than 13 Hertz). The neurologist determines the predominant frequency of a particular channel during a particular time period by measuring the period the EEG signal wave form shown on the EEG record. This requires considerable training and is highly dependent upon the skill of the neurologist, since the EEG signal wave form typically includes multiple frequency components.
EEG can be driven by specific extrinsic or endogenous events. For example, a regularly occurring stimulus will elicit a series of waves each time it is presented. The entire series is referred to as an event-related potential (ERP).
Besides the frequency of the EEG or ERP wave forms, the amplitude is often analyzed. Significance has been established when large amplitudes of brain waves occur at about 300 ms or more after the eliciting event. There is evidence to suggest that this P300 wave process is invoked when the updating, or "refreshing", of representations in working memory is required; Donchin, Psychophysioloqy, 18, 493-513 (1981); Fabiani, Karis, and Donchin, Psychophysioloqy, 22, 588-589 (1985); and others. Large P300's may be elicited by rare or unexpected events, and/or when they are relevant to a task the subject is performing as his brain activity is recorded. Such events may lead to restructuring or updating of working memory, and this activity is part of the ongoing process of maintaining accurate schema of the environment. The updating process may lead to an "activation" of the representation, or to the "marking" of some attribute of the event that was crucial in determining the updating process. This restructuring of the representation of an event is assumed to facilitate the subsequent recall of the event, by providing valuable retrieval cues, so that the greater the restructuring that follows an individual event, the higher the probability of later recalling that event. If P300 amplitude represents the degree of restructuring in working memory, then P300 amplitude should also predict later recall. Fabiani, Karis and Donchin, Psychophysiology, Vol. 23, 298-308 (1986).
In view of the current knowledge of the frequency and amplitude of brain wave forms and with the advent of widespread use of the computer in behavioral neuroscience, the analysis of data has become easier.
Oftentimes, it is desirable to have an objective method of determining whether or not a person has seen or otherwise has knowledge of a particular item, such as a weapon, a crime scene configuration, a secrete document, a stolen object, or another person's face. Such knowledge is what is taught by prior art procedures and devices used in "guilty knowledge" tests, a sub-category of procedures used in physiological detection of deception ("lie detection"). The present invention is directed to a reliable, valid easy-to-use and accurate procedure for determining guilty or other knowledge or personal beliefs on the part of an individual whose simple verbal report may be unreliable for various reasons. The present invention also may reveal concealed beliefs, attitudes, or opinions.
If a discreet stimulus, such as a sound, a light flash, or a tap, for example, is presented to a human, his electroencephalogram shows a series of time-locked responses called event related potentials (ERP). It was shown in the 1960's that if a subject is presented with a series of stimuli of two types, e.g., a high tone and a low tone, and if either of those tones is presented in 20 of 100 trials (with the remaining 80 trials containing the other tone), the rare stimulus will evoke a large ERP referred to as "P3" or previously described P300 brain wave. In this so-called "oddball" paradigm, it is known that P3 amplitude varies with rarity. Sutton, S. et al., Science, 150, 1187-1188, (1965).
In the 1970's and thereafter, other workers also using an "oddball" paradigm, reported that P3 is evoked by words (or pictures) previously seen by a subject when presented in a word (or picture) series which also includes novel words (or pictures) which fail to evoke P3. Karis, D. et al., Cognitive Psychology 16, 177-216; Neville, H. et al., Proc. Nat. Ac. Sci. U.S.A., 79, 2121-2123 (1982).
U.S. Pat. No. 4,932,416 (which is incorporated herein by reference) utilized the "oddball" method for evoking P3 as the basis of a novel set of knowledge detection procedures including guilty knowledge detection, control question testing, and other "lie detection" and related procedures.